1. Field of the Invention
The present invention relates to a device for aligning a shaft of a cutting assembly of an underwater pelletizer perpendicular to a die face in the pelletizer and more particularly to an aligning jig at the distal end of which is provided a scraper/sensor assembly. The assembly is provided with a sensor having a scraping edge to scrape low viscosity polymer drool from the die face to assure proper determination of the position of the die face so that the shaft of the cutting assembly associated therewith can be placed exactly perpendicular to the determined position of the die face.
2. Description of the Prior Art
Heretofore, in the procedure for perpendicularly aligning a shaft of a cutting assembly in a pelletizer relative to a die face in the pelletizer, a probe assembly has been utilized for determining the position of the die face. However, problems have arisen in ensuring a true reading or determination of the position of the die face due to the drool of low viscosity polymer along the die face between extrusion holes in the die face. The drool causes a probe to ride up and down relative to the die face making it very difficult to correctly determine the position of the die face relative to the shaft as the probe travels along a sweeping circular path on the die face and rides along over the drool rather than riding on the surface of the die face. In this respect, the polymer drool forms a thick coating on the die face and the probe is not supplied with any means with which it can cut through the drool to be positioned in direct contact with the die face. Such improper determination of die face position results in an incorrect alignment of the shaft of the cutting assembly which should be absolutely perpendicular to the die face so that uniformity in wear on the blades and/or die face is obtained and so that uniformity of the product (pellets) is achieved.
Various alignment techniques for aligning a shaft of a cutting assembly perpendicularly with a die face have been proposed and examples of such techniques are found in the following U.S. Patents:
______________________________________ U.S. Pat. No. PATENTEE ______________________________________ 4,021,176 Dettmer, et al. 4,179,255 Hale 4,184,833 Buchan, et al. 4,260,356 Fujiwara, et al. 4,285,652 Anders 4,290,742 Scharer, et al. ______________________________________
The Dettmer, et al. U.S. Pat. No. 4,021,176 discloses a rotating cutter for use in a pelletizer. The cutter knives are resiliently tensioned toward a die face and the cutter is adjustably mounted relative to the die in a manner to effectively minimize thermal movement of the die relative to the cutter.
The Hale U.S. Pat. No. 4,279,255 discloses a knife holder of a melt cutter apparatus which allows limited free movement of knife blades so that essentially the full length of the knife contacts the die. The limited free rotation provided coupled with low inertia of light weight flexible knives, assures contact of the knives on the die even with possible slight die deflections and nonperpendicularity of cutter drive shaft to the die face.
The Buchan, et al. U.S. Pat. No. 4,184,833 discloses a knife adjustment system comprising a knife carrier rotatably supported on a quill which is positioned on a stationary cylindrical hub which extends outwardly from a die face. A knife carrier is provided for rotation about the quill with the quill being adjustable longitudinally with respect to the hub to move the quill for adjusting the spacing between knife blades and the extruder die face.
The Fujiwara, et al. U.S. Pat. No. 4,260,356 discloses a cutting tool in a plastic dispensing apparatus which is spring biased against the surface of an extrusion block. The cutting tool further is mounted by means of a connector to a drive shaft. The connector is adapted to allow tilting of the tool to maintain a cutting edge of a blade flat against the flat surface of the extrusion block.
The Anders U.S. Pat. No. 4,285,652 discloses a gap measuring instrument with a scale which may be mounted on a blade holder of a cutting assembly. The instrument is adapted to make a complete revolution and from a reading of the gap, the position of the blades can be brought into alignment with a cutting plate by manipulating a swivel type mounting of the cutting assembly. The gap measuring instrument is not further defined.
The Scharer, et al. U.S. Pat. No. 4,290,742 discloses adjusting means for aligning the cutting plane of a set of knives with the surface of a perforated die plate of a pelletizer. The adjusting means include a ring having a wedge cross section adjustable between the mountings for the plate and the knives to vary the angular relation of the mountings.
As will be described in greater detail hereinafter, the alignment device of the present invention, comprising an alignment jig having a scraper/sensor assembly which can scape away the drool from the die face while a determination of the position of the die face is being made enables one to make a more accurate determination of die face position relative to the axis of a shaft of a cutter assembly than is provided with the prior art systems and probes referred to above.